When Tropical Cyclones Can’t Move On

SNIP: Tropical cyclones—also sometimes referred to as hurricanes and typhoons—are taking substantially longer to move from place to place, according to a new study by NCEI scientist Jim Kossin. In his paper, “A Global Slowdown of Tropical Cyclone Translation Speed (link is external),” published in Nature, Kossin demonstrates that, globally, tropical cyclones slowed by 10 percent between 1949 and 2016. With additional water vapor in the atmosphere in a warming world, as little as a 10 percent slowdown could double local rainfall and flooding impacts caused by 1°C of warming.

According to the study, tropical cyclones have slowed in both hemispheres and in every ocean basin except the Northern Indian Ocean. But, tropical cyclones have generally slowed more in the Northern Hemisphere, where more of these storms typically occur each year.

“Of great importance to society,” says Kossin, “tropical cyclones over land have slowed down 20 percent in the Atlantic, 30 percent in the western North Pacific, and 19 percent in the Australian region. These trends are almost certainly increasing local rainfall totals and freshwater flooding, which is associated with very high mortality risk.”

Hurricane Harvey in 2017 serves as a dramatic example of the consequences a slow-moving or “stalled” tropical cyclone can produce. Harvey—the hurricane that refused to leave—dumped upwards of 50 inches of rain on Houston, Texas, and the surrounding area in just five days. Some locations received two feet of rain in just two days.